1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device.
2. Description of the Related Art
In recent years, a damascene method has been used as a wiring technique for a semiconductor device in order to simplify the wiring process and to improve the yield and reliability of wiring. Further, copper has been used as a wiring material in order to reduce the resistance of the wiring.
For example, to form a multilayer copper wiring on a semiconductor substrate, a wiring groove is first formed in an interlayer insulating film formed on the semiconductor substrate. Then, the wiring groove is filled to form a copper wiring material layer. The copper wiring material layer is then planarized by chemical mechanical polishing (CMP) to form a first copper damascene wiring layer. Then, a barrier/etch stop insulating layer is deposited, covering the first copper damascene wiring layer. A second interlayer insulating film is then formed on the barrier/etch stop insulating film. Then, a photolithography technique, a dry etching technique, and an ashing technique are used to sequentially form a via hole which penetrates the second interlayer insulating film to expose the barrier/etch stop insulating film and a trench where a second copper damascene wiring layer is formed. The barrier/etch stop insulating film is removed by dry etching using a fluorocarbon gas, to expose a surface of the first copper damascene wiring layer. Subsequently, a copper wiring layer is deposited in the via hole and trench to form an interconnection plug and a second copper damascene wiring layer. Such a method of forming a copper damascene wiring layer is described in, for example, U.S. Pat. No. 6,323,121 B1.
After the barrier/etch stop insulating film has been removed by the dry etching using the fluorocarbon gas and before copper is deposited, a surface of a semiconductor wafer is often cleaned by, for example, a wet treatment. To conduct such a surface treatment, the semiconductor wafer is taken out of the dry etching apparatus after the dry etching has been finished, and transferred to a surface treatment step. Accordingly, when the semiconductor wafer is taken out of the dry etching apparatus, the exposed surface of the copper damascene wiring layer of the semiconductor wafer is exposed to the atmosphere.
As is well known in the art, copper metal is a material that is unlikely to form such a stable and dense oxide film on its surface, which may act as a protective film protecting the layer from corrosion. Thus, when the surface of the copper damascene wiring layer is exposed to the atmosphere, corrosion occurs, and the corrosion reaction is difficult to stop. Moreover, in the dry etching using the fluorocarbon etching gas, overetching is usually carried out, so that the copper damascene layer is exposed to the plasma of the fluorocarbon etching gas. As a result, fluorocarbon deposits are accumulated on the copper damascene wiring layer to attach fluorine to the copper surface. In the presence of a halogen such as fluorine which has a high electronegativity, the corrosion reaction (oxidation reaction) of the copper is expected to progress further rapidly due to reaction with moisture in the atmosphere.
The copper oxide resulting from the corrosion increases the volume of the copper damascene wiring layer, while reducing the metal copper in the copper damascene wiring layer. Consequently, when copper or tungsten is buried, defective burial or contact may result, causing the copper damascene wiring layer to be deformed. Further, when the copper oxide is subsequently removed by a cleaning treatment, a void may be created, which may remain as it is even after the burial of a buried wiring material, thus resulting in a defective contact. This may open the electric circuit or increase the resistance of the contact. These phenomena reduce the yield or reliability of the device.
There may be another cause of the contact of fluorine with the copper damascene wiring layer different from the fluorocarbon deposits on the surface of the copper damascene wiring layer. That is, when the barrier/etch stop insulating film on the copper damascene wiring layer is partially removed by the dry etching using the fluorocarbon gas, the fluorocarbon deposits adhere to the entire surface of the interlayer insulating film formed on the barrier/etch stop insulating film. When the interlayer insulating film is exposed to the atmosphere, fluorine is released from its surface. The fluorine may re-adhere to the copper damascene wiring layer to corrode the copper. Further, if the interlayer insulating film formed on the barrier/etch stop insulating film is formed of fluorine-containing silicon dioxide in particular, fluorine may also desorb from the film to further accelerate the corrosion.